Demand for high power batteries has been increasing with the commercial success of electric and hybrid vehicles. High power batteries require higher safety standards in order to prevent or at least minimize damage to people and property from catastrophic events in the batteries. To enhance safety of the battery, it is important to employ a separator having high thermally stability to prevent physical contact of the electrodes at elevated temperatures. Presently available separators are primarily based upon polyolefins such as polyethylene (PE) and polypropylene (PP). However, because PE and PP exhibit insufficient thermal stability for high power batteries, several approaches have been developed to improve thermal stability of the separator.